1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a program. In particular, the present invention relates to an image processing apparatus, an image processing method, and a program which perform image conversion on a two-dimensional image to generate a binocular disparity image capable of stereovision.
2. Description of the Related Art
To date, various proposals have been made of an apparatus and method for converting a two-dimensional image into a binocular disparity image capable of stereovision. A binocular disparity image generated on the basis of a two-dimensional image includes a pair of images for right and left eyes, observed by a right eye and by a left eye, respectively. An observer can perceive an image as a stereoscopic image by the presentation of the binocular disparity image including a pair of the images for a right eye and for a left eye using a display apparatus capable of presenting an image for a right eye and an image for a left eye separately to the observer's right eye and left eye, respectively.
Related-art techniques that have been disclosed on the generation and the display processing of such an image include the following.
For example, Japanese Unexamined Patent Application Publication No. 9-107562 has disclosed an image processing configuration for a moving image having motion in a horizontal direction. Specifically, in the image processing configuration, an original image is output to one of the images for a right eye or a left eye, and an image having a delay for each field is output to the other of the images. By such image output control, the technique allows a user to perceive an object moving horizontally to be nearer than the background.
Also, Japanese Unexamined Patent Application Publication No. 8-30806 has proposed an apparatus allowing a user to perceive that a still image or a moving image having little motion stands out by shifting the image for a right eye from the image for a left eye by a predetermined amount in the horizontal direction.
Also, Japanese Unexamined Patent Application Publication No. 10-51812 has proposed a method in which an image is divided into a plurality of disparity calculation areas, a pseudo depth is calculated for each of the areas from the feature quantity of the image, and the image for a right eye is horizontally shifted from the image for a left eye in the opposite direction on the basis of the depth.
Also, in the same manner as Japanese Unexamined Patent Application Publication No. 10-51812, Japanese Unexamined Patent Application Publication No. 2000-209614 has made a proposal to prevent eye fatigue by restricting the amount of delay in the horizontal direction while changing the amount of delays in the horizontal direction of the image for a right eye and the image for a left eye on the basis of the amount of delay calculated from the feature quantity of an image so as not to generate the binocular disparity more than necessary.
Further, Japanese Unexamined Patent Application Publication No. 2005-151534 has proposed a method in which the feature quantities of the upper section and the lower section of an image are calculated, a combination ratio of a plurality of scene structures representing depth information provided in advance is adjusted so that an image is expressed by a combination of simple structures.
The above-described related-art techniques have the problems described below.
The image conversion apparatus described in Japanese Unexamined Patent Application Publication No. 9-107562 allows only an object moving horizontally at a constant speed to be viewed stereoscopically. Binocular disparity is not correctly set for an image including a plurality of moving subjects and an image including complicated motion, and an object is placed at an unnatural position, and the retinal disparity becomes too large, thereby a stereovision is considered not to be formed.
Also, in the image conversion apparatus described in Japanese Unexamined Patent Application Publication No. 8-30806, the entire screen is only shifted for a still image or a moving image having little motion, and thus it is not possible to express a front-behind relationship between objects in the image.
In the image conversion apparatus described in Japanese Unexamined Patent Application Publication Nos. 10-51812 and 2000-209614, a pseudo depth is estimated from the feature quantity of the image. However, the estimation is based on the assumption that an object at the front of the screen has a high sharpness, a high brightness, and a high saturation, and thus the estimation is not necessarily correct. Accordingly, an incorrect retinal disparity is given to an object whose depth is incorrectly estimated, and thus the object is placed at a wrong position.
In the image conversion apparatus described in Japanese Unexamined Patent Application Publication No. 2005-151534, the structure of an image is applied to a relatively simple finite structure, and thus the occurrence of unnatural depth is restrained. However, there is a problem, being common to all the related-art methods, that relatively large retinal disparity occurs in the generated binocular disparity image. The binocular disparity image is stereoscopically displayed using a stereoscopic display apparatus. In general, an observer uses a stereoscopic display apparatus for observing an image with a pair of special glasses, such as passive glasses separating an image into images for right and left eyes, respectively, by a polarization filter or a color filter, or an active glasses separating an image into images for right and left eyes in time by liquid crystal shutters.
When viewing a binocular disparity image having large retinal disparity, an observer can perceive stereoscopic effect in accordance with the retinal disparity in a state of wearing such glasses for stereovision. However, when the observer views a screen without the glasses, the images for right and left eyes are seen as images overlapped with each other in a large way, making it difficult to be seen as a normal two-dimensional image. That is to say, the images converted by the related-art image conversion apparatuses have been appreciated only in a state of wearing the glasses.
Also, a large retinal disparity is considered to have an influence on the observer's fatigue. For example, in Japanese Unexamined Patent Application Publication No. 6-194602, a description has been given of the fact that if images for a right eye and a left eye have a large displacement, contradiction arises between the control of an angle of convergence and the adjustment of the crystalline lens in the way of seeing in a real world, and the contradiction leads to fatigue in stereovision using binocular disparity.
Also, in the image conversion apparatus described in Japanese Unexamined Patent Application Publication Nos. 10-51812, 2000-209614, and 2005-151534, a pseudo depth is estimated from an image. However, it is difficult to detect a detailed depth from one image. For example, it is not easy to estimate a depth of a minute structure, such as a branch of a tree, an electric wire, and a hair. Accordingly, it has not been possible to give stereoscopic effect on these minute subjects.